Leukemia is thought to result from the progressive accumulation of genetic lesions which result in growth factor-independent cells that cannot undergo terminal differentiation. Oncogene-induced growth factor independence of hematopoietic cell lines is often accompanied by production of cytokines such as interleukin-3 (IL-3) or granulocyte-macrophage colony stimulating factor (GM-CSF). The BCR-ABL oncogene, implicated as being critical in the induction of human chronic myelogenous leukemia, has been shown to induce growth factor-independence and cytokine secretion. The investigators have recently observed that a mutant of BCR-ABL lacking a functional SH2 domain can induce growth factor independence in hematopoietic cell lines; however, no production of IL-3 and GM-CSF was observed in cells expressing BCR-ABL-delta-SH2. Based upon this observation, the hypothesis to be examined in this proposal is whether the production of growth factors by BCR-ABL infected cells is required for development of leukemia in vivo. In testing this hypothesis, the investigators will exploit the difference they have observed between BCR-ABL and the BCR-ABL-delta-SH2 mutant. Three approaches will be used to examine the relationship between BCR-ABL-induced cytokine expression and leukemogenesis. First the investigators will determine whether the BCR-ABL-delta-SH2 mutant can produce leukemia in mice transplanted with bone marrow cells infected with a retrovirus encoding BCR-ABL-delta-SH2. Second, using a variety of approaches, the investigators will identify the regions of the IL-3 and GM-CSF promoters that are required for transcriptional activation of these genes by BCR-ABL and v-src. Third, the investigators will identify the signal transduction pathways that are used by BCR-ABL and v-src to induce the transcriptional activation of IL-3 and GM-CSF. Dominant negative mutants of ras, raf, MEK, MAP kinase, myc and ets family members will be used in this analysis. These studies will directly determine whether the production of cytokines by BCR-ABL-infected bone marrow cells is important in leukemogenesis, and provide insight into the mechanisms by which this transcriptional activation occurs. The answers to these questions will not only provide insight into the molecular basis of leukemogenesis, but may also indicate new therapeutic approaches that target these mechanisms.